I contacted BMW NA about header back exhaust, with regard to warranty. They said that they frown upon After Market products and can only say if in their opinion the after market product cause damage to OEM parts it would not be covered. When I asked for more detail he said that he had no technical knowledge as did his supervisor. BMW does not want their customer service people to have any knowledge of their cars, because they do not want them to give out advise that may be incorrect. He was willing to advise me not to buy a competitors automobile, beyond that it was a pretty pointless conversation.